Using this method, Kurbo rates normal milk, a good source of protein, calcium and vitamin D, as a red-light food.

This seems weird when more than half of Australian children aged nine to 18 are not getting the recommended levels of calcium.

Labelling foods as good or evil isn’t new, and it clearly hasn’t worked to date, so it seems unlikely putting it in app form will be any more successful.

Because foods in isolation aren’t healthy or unhealthy, our dietary patterns are. And our weight and health also depend on a whole bunch of other factors like our genes, physical activity and socio-economic status.

But isn’t it backed by science

Kurbo claims to be “science-backed”.

It’s true that the traffic light system has been researched, and used in some weight-loss clinics.

But, in these settings it isn’t used in isolation, it’s used as part of a larger package of interventions like family behavioural therapy, counselling and physical activity. So it’s not even clear if the traffic light part is what’s working.

You can’t expect to be able to pull one element out of a fully supervised clinic setting, stick it in an app and get the same result.

There has been one study — not a peer-reviewed publication but work presented at a meeting — that looked at 65 kids using the app over just three months, which isn’t many people and it’s not a long follow-up for a weight loss program.

On most programs people lose weight early, but gain it back later. App users did lose weight on average, but results, reported in change in age-adjusted body mass index (BMI) units, are small.

Depending on the height of the child, this weight loss could be just a few-hundred grams. Averages can mean some lost lots of weight and others none.

They also didn’t report on the mental health or wellbeing of participants, and the negative impacts could take much longer to become apparent.

These studies have also mostly been in white, middle-class kids so it isn’t clear if the results can be generalised to other kids.

BMI isn’t great when it comes to ethnic diversity.

But maybe they should have tested it in rich kids because, at $US69 a month, no-one else is going to be able to afford it anyway.

The testimonial trap

If it’s scientifically backed, why is it advertised with testimonials and not with data? “This person lost this many kilograms” is a common way to promote weight-loss programs.

It’s fool proof — if we join but don’t have the same success we don’t blame the diet, we just blame ourselves.

They cover themselves with the disclaimer, “Results are not typical”.

The actual science suggests the real typical results are that restrictive diets only work short term, with most gaining the weight back and ending up in a cycle of yo-yo dieting.

Even with supervision, The American Academy of Pediatrics warns against weight-loss diets for kids. They recommend focusing on family meals, limiting screen time, making fruit and veg accessible and encouraging physical activity, rather than focusing on weight. There is more to a healthy diet than weight.

Weight-loss and app industries not well-regulated

The information in apps is not vetted.

The industry relies on consumer reviews to control quality. But like most weight-loss programs, these apps are likely to work in the short term, leading to positive reviews.

But when we gain the weight back in the long-term we aren’t going to blame the app, we are more likely to blame ourselves. They keep trading on hope, the last one didn’t work for me but maybe this one will…

What should we do then?

You wouldn’t use an app to home-school your children, or to instruct you to perform dentistry procedures on them. So why would you use an app for their diets?

We all eat, so it’s easy to take the professionals for granted. If you are worried about your child’s weight or diet in Australia, you should see an Accredited Practicing Dietitian (APD).

APDs have university qualifications in nutrition and nutrition therapy. This means they consider physical health, mental wellbeing and behaviour.

They also do ongoing professional development to stay up to date with the evidence. APDs also have a code of conduct and professional standards.

They cannot use testimonials, and they won’t provide advice if it isn’t based on peer-reviewed scientific evidence.

Kids are going to eat every day for the rest of their lives — there’s no science that justifies teaching them to approach it with guilt and shame.

Emma Beckett is a molecular nutritionist in the School of Environmental and Life Sciences at Newcastle University.